1. Field of the Invention
The present invention relates to a mechanical joint assembly. It also relates to a method of manufacturing a ball joint assembly.
2. Brief Description of the Related Art
The invention is more particularly concerned with ball joint assemblies which comprise, by way of external component, a body made of a plastic matrix composite material and, by way of an internal component, a joint component such as a ball joint centerpiece, with the interposition of a metal rigid insert between this external body and this internal component. Stated differently, this kind of ball joint assembly typically corresponds to a ball joint or to a rolling bearing of which the ring known as the “outer ring” is externally covered with a composite material so that this “outer” ring ultimately corresponds to the metal insert mentioned hereinabove and is fixedly attached to the composite material, the latter forming the abovementioned external body. In practice, this external body made of composite material is shaped into highly varying structures, such as a collar, a flange analogous to a fitting or a link rod tube end or the like.
The invention thus preferably, although not exclusively, relates to the field of aeronautics in which the use of composite materials is encouraged because of their lightness of weight.
This type of ball joint assembly should not be confused with the assemblies proposed in U.S. Pat. No. 6,139,788 and the improvement WO-A-2007/009423 thereto, in which assemblies an internal ball is mounted in the manner of a ball joint inside a shell made of composite material, attached by push-fitting around the ball and is then covered with a cast metal or injection-moulded plastic external body. This structure with a composite intermediate shell makes it possible to achieve a remarkable degree of sliding between the ball and the shell, but is able to withstand only very limited mechanical stress levels otherwise there is the risk that the ball will become “dislocated” from its shell.
Likewise, the type of ball joint assembly with which the invention is concerned does not correspond to the joint structures that incorporate a synthetic packing ring covering an antifriction insert. An example of that kind of synthetic ring is given in FR-A-1 547 030. Indeed in service, these structures do not transmit any load to this synthetic ring, which in any case is designed to be soft and elastic, particularly for reasons of fit.
As far as the type of ball joint assembly to which the invention relates is concerned, an important technical restriction as far as the interface between the insert and the composite body is concerned must, however, be noted. Specifically, it is commonplace for the insert to have an exterior geometry such as that of a cylinder on a circular base, centred on the axis of symmetry of revolution of its interior surface, which in the case of a ball joint is typically spherical. That is associated with the fact that this insert, as explained hereinabove, corresponds to the “outer” ring of a ball joint or rolling bearing, the manufacture of which systematically includes a machining operation in order to bring the exterior surface of this ring to its definitive cylinder dimensions as explained in FR-A-2 796 110. That being the case, when the ball joint assembly is highly stressed, the fixed connection between the external body and the insert has a tendency to yield, through the shearing of the plastic, the demise of the body/insert interface being brought about all the more readily as a result of the cylindrical exterior geometry of the insert, particularly when the joint is loaded along the central axis of this cylindrical geometry.